Implantable medical systems and methods including pulse generators and leads

ABSTRACT

Methods for implanting a puke generator (PG) within a pectoral region of a chest of a patient and devices having the PG. The PG has a housing that includes a PG electrode. Methods also include implanting at least one lead having first and second electrode segments with the first electrode segment positioned along an anterior of the chest of the patient and the second electrode segment positioned along at least one of a posterior of the patient or a side of the patient. The first and second electrode segments are positioned subcutaneously at or below an apex of a heart of the patient, wherein the PG electrode and the first and second electrode segments are configured to provide electrical shocks for antiarrhythmic therapy.

BACKGROUND

Embodiments of the present disclosure relate generally to subcutaneousimplantable medical devices and methods, and more particularly tomedical devices having pulse generators and leads that are implantedsubcutaneously.

Currently, implantable medical devices (IMD) are provided for a varietyof cardiac applications. IMDs may include a “housing” or “canister” (or“can”) and one or more electrically-conductive leads that connect to thecanister through an electro-mechanical connection. IMDs may containelectronics (e.g., a power source, microprocessor, capacitors, etc.)that control electrical activation of the leads to provide variousfunctionalities. For instance, the IMD may be configured for pacemaking,cardioversion, and/or defibrillation. An implantablecardioverter-defibrillator (ICD) is one such medical device and it isdesigned to monitor heart rate, recognize certain events (e.g.,ventricular fibrillation or ventricular tachycardia), and deliverelectrical shock to reduce the risk of sudden cardiac death (SCD) fromthese events. The ICD may be used for patients who have alreadyexperienced potentially life-threatening events or for those that are atrisk of SCD. The ICD includes a pulse generator and one or more leadshaving electrodes that may be used to detect how the heart isfunctioning or provide electrical shock to the heart.

One type of ICD delivers therapy through transvenous leads that areadvanced to the right ventricle for detection and treatment oftachyarrhythmia. Transvenous ICDs (or TV-ICDs) may also providebradycardia-pacing support. Although TV-ICDs can be helpful and preventsudden cardiac death, TV-ICDs may have certain drawbacks or potentialcomplications. For instance, it can be difficult and time-consuming toachieve venous access, thereby prolonging the medical procedure. TV-ICDscan be associated with hemopericardium, hemothorax, pneumothorax, leaddislodgement, lead malfunction, device-related infection, and venousocclusion. Transvenous leads may also malfunction through conductorfailure in the leads or breaches in the insulation that surrounds theconductors.

A second type of ICD, referred to as a subcutaneous ICD (or S-ICD), usesan electrode configuration that can reside entirely within thesubcutaneous space. The pulse generator is positioned along a side ofthe patient's chest below the arm pit (e.g., over the sixth rib near theleft mid-axillary line). A lead extends from the pulse generator alongthe side of the patient toward the sternum. The lead then turns toextend parallel to the mid-sternal line and is positioned adjacent tothe sternum extending between the xiphoid process and themanubriosternal junction. This portion of the lead includes a shock coilthat is flanked by two sensing electrodes. The sensing electrodes sensethe cardiac rhythm and the shock coil delivers counter-shocks throughthe subcutaneous tissue of the chest wall. Unlike the transvenous types,the S-ICDs lack intravenous and intracardiac leads and, as such, areless likely to have the noted complications associated with moreinvasive devices. Current electrode configurations for S-ICDs, however,have some challenges or undesirable features. For instance, S-ICDstypically have a relatively large canister (e.g., about 70 cc) toprovide a sufficient amount of energy for defibrillation.

Accordingly, a need remains for alternative S-ICD electrodeconfigurations that provide a sufficient amount of energy fordefibrillation.

SUMMARY

Embodiments set forth herein include implantable medical devices(SIMDs), systems that include SIMD, and methods of using and positioningthe same. SIMDs may include a pulse generator and at least one lead. Theat least one lead may have multiple segments. The segments may beseparate or may be portions of a single elongated coil. In someembodiments, the entire SIMD may be positioned subcutaneously (e.g.,beneath the skin but above layers of skeletal muscle tissue, rib bones,and costal cartilage). In some embodiments, only designated elements ofthe SIMD are positioned subcutaneously. In other embodiments, at leastsome elements of the SIMD may be positioned submuscularly. For example,the pulse generator may be implanted submuscularly (e.g., under theserratus anterior muscle) or under the serratus anterior fascia butabove muscle.

In accordance with one or more embodiments herein, a method is providedthat includes implanting a pulse generator (PG) within a pectoral regionof a chest of a patient. The PG has a housing that includes a PGelectrode. The method also includes implanting at least one lead havingfirst and second electrode segments with the first electrode segmentpositioned along an anterior of the chest of the patient and the secondelectrode segment positioned along at least one of a posterior of thepatient or a side of the patient. The first and second electrodesegments are positioned subcutaneously at or below an apex of a heart ofthe patient, wherein the PG electrode and the first and second electrodesegments are configured to provide electrical shocks for antiarrhythmictherapy.

In some aspects, the first and second electrode segments are portions ofa common lead coil that extends from a proximal end of the firstelectrode segment to a distal end of the second electrode segment. Thecommon lead coil extends along the chest of the patient from theanterior of the chest toward the side of the patient, wherein the secondelectrode segment extends to or beyond a midaxillary line of thepatient.

In some aspects, an active length of the common lead coil is at least 35cm from the proximal end of the first electrode segment to the distalend of the second electrode segment.

In some aspects, the first and second electrode segments are spacedapart from one another, the second electrode segment being longer thanthe first electrode segment. Optionally, the second electrode segmenthas an active length measured between proximal and distal ends of thesecond electrode segment. The active length is at least 12 centimeters(cm), wherein the second electrode segment extends beyond a posterioraxillary line.

In some aspects, it the at least one lead includes positioning one leadsuch that the one lead extends away from the pulse generator,extra-thoracically along the sternum, and along an intercostal gap sothat a distal end of the one lead is positioned at or beyond amidaxillary line of the patient.

In some aspects, implanting the first electrode segment includestunneling from a pocket where the pulse generator is positioned along asternum of the patient to an intercostal gap at or below the apex of theheart.

In some aspects, implanting the second electrode segment includes makinga tunnel that extends along an intercostal gap between a first accessincision proximate to the xiphoid process and a second access incisionthat is positioned at or beyond a midaxillary line.

In some aspects, implanting the pulse generator includes making asubcutaneous pocket and positioning the pulse generator within thesubcutaneous pocket.

In some aspects, the first and second electrode segments are portions ofa continuous elongated body that wraps about the patient, whereinimplanting the first electrode segment and the second electrode segmentincludes making a xiphoid incision and an access incision at or beyond amidaxillary line near an intercostal gap.

In some aspects, the first electrode segment has an active length thatextends between a proximal end and a distal end of the first electrodesegment. The active length is between 5 and 12 cm.

In some aspects, a defibrillation threshold (DFT) is at most 50 Joulesand a volume of the pulse generator is at most 40 milliliters.

In accordance with one or more embodiments herein, a subcutaneousimplantable medical system is provided that includes a pulse generator(PG) configured to be positioned subcutaneously within a pectoral regionof a chest of a patient. The PG has a housing that includes a PGelectrode. The PG has an electronics module. The subcutaneousimplantable medical system also includes an elongated lead that iselectrically coupled to the pulse generator. The elongated lead includesa first electrode segment that is configured to be positioned along ananterior of the chest of the patient and a second electrode segment thatis configured to be positioned along at least one of a posterior of thepatient or a side of the patient. An active length of the lead bodyextends between a proximal end of the first electrode segment and adistal end of the second electrode segment. The active length is atleast 35 centimeters (cm), wherein the electronics module is configuredto provide electrical shocks for antiarrhythmic therapy using the PGelectrode and the first and second electrode segments.

In some aspects, the first and second electrode segments are portions ofa common lead coil that extends from a proximal end of the firstelectrode segment to a distal end of the second electrode segment. Thelead coil is sized to extend along the chest of the patient from theanterior of the chest to the posterior of the patient. An active lengthof the common lead coil is at least 35 cm from the proximal end of thefirst electrode segment to the distal end of the second electrodesegment.

In some aspects, the first and second electrode segments are spacedapart from one another. The second electrode segment is longer than thefirst electrode segment. The second electrode segment has an activelength measured between proximal and distal ends of the second electrodesegment. The active length is at least 12 cm, wherein the secondelectrode segment extends beyond a posterior axillary line.

In some aspects, the first electrode segment has an active lengthmeasured between proximal and distal ends of the first electrodesegment. The active length is between 5 and 12 cm.

In some aspects, a defibrillation threshold (DFT) is at most 50 Joulesand a volume of the PG is at most 40 milliliters.

In accordance with one or more embodiments herein, a method of treatinga patient is provided. The method includes sensing cardiac activity of apatient with a subcutaneous implantable medical system. The subcutaneousimplantable medical system includes a pulse generator (PG) positionedsubcutaneously within a pectoral region of a chest of the patient. Thesubcutaneous implantable medical system also includes a first electrodesegment positioned along an anterior of the chest of the patient and asecond electrode segment positioned along at least one of a posterior ofthe patient or a side of the patient. The first and second electrodesegments are positioned subcutaneously at or below an apex of a heart ofthe patient. The method also includes providing antiarrhythmic therapy,based on the cardiac activity, by providing electrical shocks or pulsesbetween the first and second electrode segments and an electrode of thePG.

In some aspects, the first and second electrode segments are portions ofa common lead coil that extends from a proximal end of the firstelectrode segment to a distal end of the second electrode segment. Thelead coil extends along the chest of the patient from the anterior ofthe chest to the posterior of the patient. An active length of thecommon lead coil is at least 35 cm from the proximal end of the firstelectrode segment to the distal end of the second electrode segment.

In some aspects, the first and second electrode segments are spacedapart from one another. The second electrode segment is longer than thefirst electrode segment. The second electrode segment has a length thatis at least 12 centimeters (cm), wherein a defibrillation threshold(DFT) is at most 50 Joules and a volume of the PG is at most 40milliliters.

In accordance with one or more embodiments herein, a method is providedthat includes implanting a pulse generator (PG) within a pectoral regionof a chest of a patient. The PG has a housing that includes a PGelectrode. The method also includes implanting at least one lead havinga common lead coil that extends from a proximal end to a distal end. Theproximal end position along an anterior of the chest of the patient, andthe distal end positioned along at least one of a posterior or a side ofthe patient. The common lead coil is positioned subcutaneously. At leasta majority of the common lead coil is positioned at or below an apex ofa heart of the patient, wherein the PG electrode and the common leadcoil are configured to provide electrical shocks for antiarrhythmictherapy.

In some aspects, the common lead coil extends along the chest of thepatient from the anterior of the chest to the distal end, wherein thedistal end is positioned at or beyond the midaxillary line of thepatient. In certain aspects, the distal end is positioned at or beyond aposterior axillary line of the patient.

In some aspects, an active length of the common lead coil is at least 35cm from the proximal end to the distal end.

In accordance with one or more embodiments herein, a subcutaneousimplantable medical system is provided that includes a pulse generator(PG) configured to be positioned subcutaneously within a pectoral regionof a chest of a patient. The PG has a housing that includes a PGelectrode. The PG has an electronics module. The subcutaneousimplantable medical system also includes an elongated lead that iselectrically coupled to the pulse generator. The elongated lead includesa common lead coil that extends between a proximal end and a distal end.The proximal end is configured to be positioned along an anterior of thechest of the patient, and the distal end is configured to be positionedalong a posterior of the patient or a side of the patient. The commonlead coil is configured to be positioned subcutaneously. At least amajority of the common lead coil is configured to be positioned at orbelow an apex of a heart of the patient. The electronics module isconfigured to provide electrical shocks for antiarrhythmic therapy usingthe PG electrode and the common lead coil.

In some aspects, an active length of the common lead coil is at least 35cm from the proximal end to the distal end.

In accordance with one or more embodiments herein, a method of treatinga patient is provided. The method includes sensing cardiac activity of apatient with a subcutaneous implantable medical system. The subcutaneousimplantable medical system includes a pulse generator (PG) positionedsubcutaneously within a pectoral region of a chest of the patient. Thesubcutaneous implantable medical system also includes a common lead coilthat extends between a proximal end and a distal end. The common leadcoil is positioned subcutaneously. At least a majority of the commonlead coil is positioned at or below an apex of a heart of the patient,wherein the PG electrode and the common lead coil are configured toprovide electrical shocks for antiarrhythmic therapy. The method alsoincludes providing antiarrhythmic therapy, based on the cardiacactivity, by providing electrical shocks or pulses between the commonlead coil and an electrode of the PG.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a graphical representation of a heart with animplantable medical system for providing defibrillation and optionallyother therapy.

FIG. 2 illustrates a simple block diagram of at least a portion of thecircuitry within a subcutaneous implantable medical device (SIMD) inaccordance with an embodiment herein that may be used with the system ofFIG. 1.

FIG. 3A illustrates an anterior view of a patient, including therelative positions of a pulse generator (PG) electrode and an elongatedcoil in accordance with an embodiment.

FIG. 3B is a side view of the patient illustrating the PG electrode andthe elongated coil.

FIG. 4 illustrates relative positions of an electrode of a pulsegenerator (PG) and multiple coils segments positioned relative to aheart of a patient.

FIG. 5 illustrates relative positions of a PG electrode and multiplecons segments positioned relative to a heart of a patient, including aparasternal electrode segment.

FIG. 6 illustrates a flow chart for implanting a subcutaneous medicalsystem in accordance with an embodiment.

FIG. 7 illustrates a block diagram of an SIMD in accordance with anembodiment that is capable of performing stimulation therapy, includingcardioversion, defibrillation, and pacing stimulation.

DETAILED DESCRIPTION

Embodiments set forth herein include implantable medical devices(SIMDs), systems that include SIMD, and methods of using and positioningthe same. In particular embodiments, the SIMD includes a subcutaneousimplantable cardioverter-defibrillator (S-ICD). Embodiments include apulse generator that is positioned within a pectoral region of a chestof a patient. The PG has a housing or canister that includes a PGelectrode. Embodiments also include at least one lead having first andsecond electrode segments with the first electrode segment positionedalong an anterior of the chest of the patient and the second electrodesegment positioned along a posterior of the patient. Optionally,embodiments may include additional electrode segments, such as a thirdor fourth electrode segment. For example, in some embodiments, thesecond electrode segment may comprise two electrode sub-segments.

An electrode segment represents an electrically conductive portion ofthe lead that is operable to deliver energy for antiarrhythmic therapy.An electrode segment may be, for example, a coil electrode, a ringelectrode, or the like. As used herein, an “electrode segment” mayrepresent a portion of a larger electrode or may be a discrete electrodethat is spaced apart from other electrode segments. In such instances,the discrete electrode segments may be attached to the same lead ordifferent leads. In particular embodiments, electrode segments may beportions of a common (or same) lead coil. For example, a first portionof the common lead coil (or first electrode segment) may be positionedalong an anterior of the chest and a second portion of the common leadcoil (or second electrode segment) may be positioned along a posteriorof the patient. An intermediate electrode segment of the common leadcoil may extend between the first and second electrode segments. Thus,the common lead coil may extend continuously from the anterior of thechest to the posterior of the patient.

For the avoidance of doubt, a claim reciting a “first electrode segment”and a “second electrode segment” does not preclude additional electrodesegments (e.g., a third electrode segment or a fourth electrode segmentor so forth). Such additional electrode segments may be positioned alongthe anterior of the chest, a lateral region of the patient, or theposterior of the patient.

The PG electrode and the first and second electrode segments mayreliably provide a sufficient amount of energy for antiarrhythmictherapy (e.g., defibrillation). Embodiments may enable pulse generatorswith defibrillation thresholds (DFTs) that are less than known systems.For example, the DFT in some embodiments may be at most 50 Joules. TheDFT in certain embodiments may be at most 45 Joules or, moreparticularly, at most 40 Joules. Embodiments may also enable using pulsegenerators or canisters with a smaller volume than known systems. Forinstance, a volume of the pulse generator may be at most 40 millilitersor at most 35 milliliters.

As used herein, the term “subcutaneously,” when used to describeimplanting a device (e.g., pulse generator, lead body, electrode, etc.),means implanting the device beneath the skin but above layers ofskeletal muscle tissue, rib bones, and costal cartilage. The device istypically positioned under the subcutaneous tissue. When the term“subcutaneous” is used to characterize the entire implantable medicalsystem, the term means that most of the operating components of thesystem (e.g., the pulse generator, shocking electrodes, optional sensingelectrodes, lead bodies) or each and every one of the operatingcomponents is beneath the skin, but above layers of skeletal muscletissue, rib bones, and costal cartilage. Compared to transvenous ICDimplantation, subcutaneous implantation may be less complex, lessinvasive, and less time-consuming. In some embodiments, however, one ormore components may not be subcutaneous. For example, additionalelectrodes may be used that are transvenous or that contact outercardiac tissue. In alternative embodiments, the pulse generator may beimplanted submuscularly (e.g., under the serratus anterior muscle) orunder the serratus anterior fascia but above muscle.

FIG. 1 illustrates a graphical representation of an implantable medicalsystem 12 that is configured to apply therapy to a heart. In particularembodiments, the system 12 may apply pacing therapy, cardiacresynchronization therapy (CRT) and general arrhythmia therapy,including defibrillation. The system 12 includes a subcutaneousimplantable medical device (SIMD) 14 that is configured to be implantedin a subcutaneous area exterior to the heart. The SIMD 14 is positionedin a subcutaneous area or region.

In the illustrated embodiment, the system 12 includes only the SIMD andis entirely or fully subcutaneous. The system 12 does not requireinsertion of a transvenous lead. It is contemplated, however, thatsystem 12 may include other components. For example, alternativeembodiments may include a transvenous lead or a leadless electrode.

The SIMD 14 includes a pulse generator 15 and at least one lead 20 thatis operably coupled to the pulse generator 15. The “at least one lead”is hereinafter referred to as “the lead.” Nevertheless, it should beunderstood that the term, “the lead,” may mean only a single lead or maymean more than one single lead. The lead 20 includes at least oneelectrode segment that is used for providing electrical shocks fordefibrillation. Optionally, the lead 20 may include one or more sensingelectrodes. The pulse generator 15 may be implanted subcutaneously andat least a portion of the lead 20 may be implanted subcutaneously. Inparticular embodiments, the SIMD 14 is an entirely or fully subcutaneousSIMD. In FIG. 1, the SIMD 14 is positioned within a pectoral region.Optionally, the SIMD 14 may be positioned in a different subcutaneousregion. The SIMD 14 may detect or sense cardiac activity (e.g., cardiacrhythm). The SIMD 14 is configured to deliver various arrhythmiatherapies, such as defibrillation therapy, pacing therapy,antitachycardia pacing therapy, cardioversion therapy, and the like,based on the cardiac activity.

The pulse generator 15 includes a housing or canister 18. The pulsegenerator 15 is configured to be connected to the lead 20 of the system12. The pulse generator 15 also includes a pulse-generator (PG)electrode 19. As used herein, a pulse generator or a housing of thepulse generator “includes an electrode” when the housing forms orconstitutes the electrode or when the housing (or other part of thepulse generator) has a discrete electrode attached thereto. Inparticular embodiments, the housing 18 forms the PG electrode 19.

The lead 20 includes an elongated lead body 60 that extends from aPG-end portion 62 to a distal tip 64. The PG-end portion 62 is operablyconnected to the pulse generator 15 in FIG. 1. The PG-end portion 62 mayinclude one or more electrodes (not shown) that electrically engagerespective terminals (not shown) of the pulse generator 15. Morespecifically, the PG-end portion 62 may be inserted into a port of thepulse generator 15 where the terminals are located.

The elongated lead body 60 includes an elongated flexible tube or sleeve66 comprising, for example, a biocompatible material (e.g.,polyurethane, silicone, etc.). The lead body 60 may include a singlelumen (or passage) or multiple lumen (or passages) within the flexibletube 66. The lead 20 also includes a plurality of electrical conductors(not shown) that electrically couple the shocking electrode segments(and optionally sensing electrodes) to the pulse generator 15. Theelectrical conductors may be cabled conductors coated with PTFE(poly-tetrafluoroethylene) and/or ETFE (ethylenetetrafluoroethylene).The lead body 60 may be configured for receiving a stylet that enablespositioning of the lead. The electrical conductors are terminated to therespective electrode segments. For example, the conductors may beterminated to respective electrodes of the PG-end portion 62 and thenrespective electrode segments 22, 24 (described below).

As described above, the lead 20 may include one or more electrodesegments. As shown, the lead 20 includes electrode segments 22, 24 inwhich the electrode segments 22, 24 are spaced apart from one anotherhaving an electrical gap 74 therebetween. The lead body 60 may extendbetween the gap 74. The electrode segments 22, 24 may be referred to asfirst and second electrode segments 22, 24. The electrode segment 22 maybe positioned along an anterior of the chest. The electrode segment 24may be positioned along a lateral and/or posterior region of thepatient. The electrode segments 22, 24 may be portions of the same lead,or the electrode segments may be portions of different leads. Theelectrode segments 22, 24 may be positioned subcutaneously at a levelthat aligns with the heart of the patient for providing a sufficientamount of energy for defibrillation. For example, the electrode segments22, 24 may be positioned at or below an apex of the heart.

In some embodiments, the lead 20 includes an elongated, common lead coil70 that includes the electrode segments 22, 24. The electrode segments22, 24 are portions of the common lead coil 70. In FIG. 1, the commonlead coil 70 extends continuously from a proximal end 23 of theelectrode segment 22 to a distal end 25 of the second electrode segment24. The distal end 25 coincides with the distal tip 64 in FIG. 1. Aproximal end of an electrode segment is the end that is closest to thePG along a path of the lead. A distal end of an electrode segment is theend that is furthest from the PG along the path of the lead. The commonlead coil 70 is represented by the electrode segments 22, 24 and anintermediate electrode segment 72 (indicated by dashed ones) thatextends between the cons segments 22, 24. More specifically, the commonlead coil 70 may be only a single coil electrode that extendscontinuously (e.g., without interruption) from the proximal end 23 tothe distal end 25. In such embodiments, the segments may beindistinguishable.

Alternatively, the electrode segments 22, 24 may be discrete segmentsthat are spaced apart from one another along the lead body 60 or thatare positioned along different leads. For example, the electrode segment22 may be positioned along the anterior of the chest. The lead body 60may extend from a distal end of the electrode segment 22 to a proximalend of the electrode segment 24. As such, the gap 74 exists between theelectrode segments 22, 24 along a length of the lead body 60. A lengthof the gap 74 may be, for example, at least 10 centimeters (cm). Incertain embodiments, the length of the gap 74 may be at least 12 cm, atleast 14 cm, or at least 16 cm. In particular embodiments, the length ofthe gap 74 may be at least 18 cm or at least 20 cm.

The electrode segments 22, 24 (or the common lead coil 70) may bepositioned subcutaneously at a level that is suitable for providing asufficient amount of energy for defibrillation. For example, theelectrode segments 22, 24 (or the common lead coil 70) may be positionedsubcutaneously at a level that approximately aligns with an apex of aheart of the patient. The electrode segments 22, 24 may be positioned ator below the apex of the heart. For example, the electrode segments 22,24 (or the common lead coil 70) may be positioned along an intercostalgap between the seventh and eighth ribs of the patient or along anintercostal gap between the sixth and seventh ribs of the patient. It iscontemplated, however, that the electrode segments 22, 24 (or the commonlead coil 70) may be positioned at other levels with respect to theheart.

Optionally, the electrode segments 22, 24 and the PG electrode 19 (orthe housing 18) may be configured to perform sensing (along one or moresensing vectors) and to deliver various types of therapy. The lead 20 ispositioned such that the electrode segments 22 and 24 are positionedproximate to (but outside of) various regions or chambers of the heart.In the example of FIG. 1, the SIMD 14 is positioned above the heart,while the electrode segment 22 is positioned at a level that isapproximately equal to the apex. The electrode segment 24 may bepositioned along a lateral region and/or a posterior of the patient.Optionally, the housing 18 of the SIMD 14 may include one or moreelectrically separate electrodes, where one combination of electrodescooperates cooperate to perform sensing and the same or a differentcombination of electrodes cooperates to deliver therapy.

FIG. 2 illustrates a simple block diagram of at least a portion of thecircuitry within the SIMD 14. The SIMD 14 includes a controller 30 thatmay be coupled to cardiac sensing circuitry 32 and pulse sensingcircuitry 34. The controller 30 also utilizes or communicates withvarious other electronic components, firmware, software, and the likethat generally perform sensing and pacing functions (as generallydenoted by a pacemaker functional block 36). While the examples hereinare provided for pacing and defibrillation functions, the SIMD could beprogrammed to perform anti-tachycardia pacing, cardiac rhythm therapy,and the like. The cardiac sensing circuitry 32 is configured to detectone or more cardiac events (e.g., ventricular fibrillation, ventriculartachycardia, or other arrhythmia). The pulse sensing circuitry 34 isconfigured to detect event markers.

The controller 30 is configured to analyze incoming paced cardiac events(as sensed over the cardiac sensing circuitry 32). Based on thisanalysis, the controller 30 in the SIMD 14 may perform various pacemakerrelated actions, such as setting or ending timers, recording data,delivery of therapy, and the like. The controller 30 of the SIMD 14 mayalso perform various cardioversion/defibrillation related functions. Inthe example of FIG. 2, outputs 38 and 40 represent output terminals thatare coupled through a switching circuit (in the functional module 36) tocorresponding electrodes on the housing of the SIMD 14. Alternatively,the outputs 38 and 40 may be coupled to respective electrode segments onalong the lead 20 (FIG. 1).

Inputs 42-48 are provided to the cardiac and pulse sensing circuitry 32and 34. By way of example, with reference to SIMD 14, inputs 42 and 44may be coupled to sensing electrodes that supply sensed signals to asensing amplifier 52. Inputs 46 and 48 may be coupled to the same ordifferent sensing electrodes to provide sensed signals to a pulseamplifier 54. An output of the sensing amplifier 52 is supplied toamplitude discriminator 56, while an output of the pulse amplifier 54 issupplied to amplitude discriminator 58. Outputs of the amplitudediscriminators 56 and 58 are then provided to the controller 30 forsubsequent analysis and appropriate actions. The inputs 42 and 44 may becoupled to various combinations of the electrode segments 22, 24 or thePG electrode 19.

FIGS. 3A and 3B illustrate one configuration of an implantable medicalsystem 100 in accordance with an embodiment. FIG. 3A illustrates thepatient's torso and, particularly, the rib cage and the heart. In FIG.3B, only the rib cage and the heart are shown. The implantable medicalsystem 100 includes a subcutaneous implantable device (SIMD) 102 havinga pulse generator 104 positioned within a pocket 108 of a pectoralregion of a patient 101. The pocket 108 may be a subcutaneous pocketpositioned below subcutaneous tissue but above muscle tissue. Inalternative embodiments, the pocket may be submuscular (e.g., beneaththe pectoral muscle).

The pulse generator 104 includes a housing and/or electrode 105 of thepulse generator 104. In the illustrated embodiment, a single lead 110 iscoupled to the pulse generator 104 within the pocket 108. The lead 110includes a lead body 111 and an elongated lead coil 114. As shown, thelead 110 extends from the pocket 108 in the pectoral region andextra-thoracically along the sternum (e.g., over the sternum orparasternally within one to three centimeters from the sternum). Aproximal end 112 of the elongated lead coil 114 is located proximate tothe xiphoid process. As shown, the proximal end 112 is positioned alongthe anterior of the chest on a right side of the sternum. Thus, in someembodiments, the lead 110 may cross over a mid-sternal line that extendsthrough a center of the sternum.

The elongated lead coil 114 has an active length that is measuredbetween the proximal end 112 and a distal end 113. The active lengthrepresents a length of the electrode (e.g., a coil electrode) along thelead. As shown, the elongated lead coil 114 extends from proximate tothe xiphoid process, along the anterior and side of the patient withinan intercostal gap, and along the posterior of the patient toward thespine. As such, the elongated lead coil 114 may wrap about the chest ortorso of the patient. The distal end 113 may be positioned proximate toa scapula of the patient. For example, the distal end 113 may bepositioned within the intercostal gap and proximate to the tip or theinferior angle of the scapula. The distal end 113 may be positionedbetween a midaxillary line and a posterior axillary line of the patient.The midaxillary line is a coronal line extending along a surface of thebody passing through an apex of the axilla. The posterior axillary lineis a coronal line extending parallel to the midaxillary line and throughthe posterior axillary skinfold. In some instances, the distal end 113may be positioned beyond the posterior axillary line of the patient.

The elongated lead coil 114 may be characterized as having a firstelectrode segment 116 that includes the proximal end 112, and a secondelectrode segment 118 that includes the distal end 113. For embodimentsin which the elongated lead coil 114 extends substantially continuouslyfrom the proximal end 112 to the distal end 113, the elongated lead coil114 may also have an intermediate electrode segment 122 that extendsbetween the first and second electrode segments 116, 118. The first andsecond electrode segments 116, 118 and the intermediate segment 122 maybe indistinguishable such that the elongated coil 114 extendscontinuously between the proximal end 112 and the distal end 113.Alternatively, the intermediate electrode segment 122 may be discretewith respect to the first and second electrode segments 116, 118 suchthat gaps or spacings exist between the electrode segments.

In some embodiments, at least one of the electrode segments 116, 118,122 is a shock coil and at least one of the electrode segments 116, 118,122 is a sensing electrode. In other embodiments, each of the firstelectrode segment 116, the second electrode segment 118, and theintermediate segment 122 is a shock coil. In certain embodiments, thefirst electrode segment 116, the second electrode segment 118, and/orthe intermediate segment 122 are electrically common (have samepolarity) with one another.

As shown in FIG. 3B, the elongated lead coil 114 is positioned at orbelow an apex of a heart of the patient. Different portions of the leadcoil 114 may have different heights or elevations relative to the heart.In certain embodiments, each of the first electrode segment 116, thesecond electrode segment 118, and the intermediate electrode segment 122may be positioned at or below the apex. FIG. 3B identifies the apex andillustrates a transverse plane P that intersects the apex. In someembodiments, a small portion of the elongated coil 114 (or the firstelectrode segment 116) including the proximal lend 112 and/or a smallportion of the elongated coil 114 (or the second electrode segment 118)including the distal end 113 may be positioned above the transverseplane P. Nonetheless, a majority of the elongated coil 114 is positionedabove the apex of the heart. In particular embodiments, at least 75% ofthe elongated coil 114 or, more particularly, at least 85% of theelongated coil 114, more particularly, at least 95% of the elongatedcoil 114 is positioned at or below the apex. In certain embodiments, amajority of each of the first and second electrode segments 116 and 118are positioned below the transverse plane P. As described herein, theelongated lead coil 114 may be positioned subcutaneously.

In FIG. 3B, the first electrode segment 116 is at or below the apex ofthe heart, and the second electrode segment 118 is at or below the apexof the heart. A portion of the second electrode segment 118, such asless than 50% or less than 35%, may be positioned above the plane P. Inan alternative embodiment, a majority of the second electrode segment118 may be positioned above the plane P.

In the illustrated embodiment, the elongated coil 114 extends throughthe same intercostal gap from the side or lateral portion of the patientto the posterior of the patient. Optionally, the elongated coil 114 mayextend over a rib to move from one intercostal gap to anotherintercostal gap. In some cases, one or more portions of the elongatedcoil 114 may be positioned higher, such as even or level with amid-plane extending through the heart.

In some embodiments, the active length of the elongated lead coil 114 isat least thirty (30) centimeters (cm). In particular embodiments, theactive length of the elongated lead coil 114 may be at least thirty-five(35) cm. In more particular embodiments, the active length of theelongated lead coil 114 may be at least forty (40) cm. The active lengthof the elongated lead coil 114 may be at most fifty (50) cm or at mostforty-five (45) cm. Accordingly, embodiments may include a lead having asingle elongated coil (e.g., coil electrode) that has an active lengthof at least 30 cm extending from anterior to posterior of the patientwhile wrapping about a side (or lateral portion) of the chest.

FIG. 4 illustrates one configuration of an implantable medical system200 in accordance with an embodiment. The implantable medical system 200may include features that are similar or identical to the implantablemedical system 12 (FIG. 1) and/or the implantable medical system 100(FIG. 3A). For example, the implantable medical system 200 includes asubcutaneous implantable device (SIMD) 202 having a pulse generator 204positioned within a pocket 208 of a pectoral region of a patient 201.The pulse generator 204 includes a housing and/or electrode 205 of thepulse generator 204. In the illustrated embodiment, a lead 210 iscoupled to the pulse generator 204 within the pocket 208. The lead 210extends from the pocket 208 in the pectoral region andextra-thoracically along the sternum (e.g., over the sternum orparasternally within one to three centimeters from the sternum) towardthe xiphoid process.

As shown, the lead 210 may include a series of interconnected segments.For example, the lead 210 includes a first lead segment 230, a firstelectrode segment 232, a second lead segment 234, and a second electrodesegment 236. The first and second lead segments 230, 234 representinactive portions of the lead 210 that do not provide electrical shock.More specifically, the first and second lead segments 230, 234 do notinclude electrodes that are configured to form the shock vector. Thefirst electrode segment 232 has a proximal end 231 and a distal end 233.The second electrode segment 236 has a proximal end 235 and a distal end237.

The first lead segment 230 extends between the pulse generator 204 andthe first electrode segment 232. The first electrode segment 232 extendsacross the chest and is positioned subcutaneously at a level thatapproximately aligns with an apex of a heart of the patient. Theproximal end 231 of the first electrode segment 232 is located proximateto the xiphoid process and/or a mid-sternal line. The first electrodesegment 232 has an active length that extends between the proximal end231 and the distal end 233. For example, the active length of the firstelectrode segment 232 in some embodiments is between 5 cm and 12 cm. Inmore particular embodiments, the active length of the first electrodesegment 232 is between 5 cm and 8 cm.

The second lead segment 234 extends between the first electrode segment232 and the second electrode segment 236. The second lead segment 234forms a gap that separates the first and second electrode segments 232,236. A length of the second lead segment 234 may be based on desiredpositions and active lengths of the first and second electrode segments232, 236. Optionally, each of the first electrode segment 232, thesecond lead segment 234, and the second electrode segment 236 arepositioned within the same intercostal gap.

The second electrode segment 236 is positioned subcutaneously at a levelthat approximately aligns with an apex of a heart of the patient. Forexample, each of the electrode segments 230, 236 may be positioned at orbelow the apex of the heart. As shown, the second electrode segment 236extends from the proximal end 235, which is positioned at ananterior-lateral location of the patient, to the distal end 237, whichis positioned at a posterior-lateral location. More specifically, thedistal end 237 may be positioned at or beyond a midaxillary line of thepatient. The second electrode segment 236 extends within an intercostalgap of the ribs and along a side of the chest or torso. The secondelectrode segment 236 has an active length that extends between theproximal end 235 and the distal end 237. For example, the active lengthof the second electrode segment 236, in some embodiments, may be atleast 12 cm. In other embodiments, the second electrode segment 236 mayextend further along the posterior (e.g., toward the scapula) and/orfurther along the anterior (e.g., begin closer to the first electrodesegment 234). In some embodiments, the first electrode segment 234 andthe second electrode segment 236 may be electrically common (have thesame polarity).

Optionally, the first and second lead segments 230, 234 may have one ormore sensing electrodes. Optionally, the first and second electrodesegments 232, 236 may have one or more sensing electrodes.

During operation, the PG electrode 205 functions as a shockingelectrode, and the first electrode segment 234 and the second electrodesegment 236 may be electrically common (e.g., have same polarity). Ashock vector is directed from the PG electrode 206 to the firstelectrode segment 234 and the second electrode segment 236. In someembodiments, the shock vector may be reversed. In other embodiments, thefirst electrode segment 234 or the second electrode segment 236 may becommon with the PG electrode 205.

FIG. 5 illustrates one configuration of an implantable medical system300 in accordance with an embodiment. The implantable medical system 300may include features that are similar or identical to the implantablemedical system 12 (FIG. 1), the implantable medical system 100 (FIG.3A), and/or the implantable medical system 200 (FIG. 4). For example,the implantable medical system 300 includes a subcutaneous implantabledevice (SIMD) 302 having a pulse generator 304 positioned within apocket 308 of a pectoral region of a patient 301. The pulse generator304 includes a housing and/or electrode 305 of the pulse generator 304.In the illustrated embodiment, a lead 310 is coupled to the pulsegenerator 304 within the pocket 308. The lead 310 extends from thepocket 308 in the pectoral region along the sternum of the patient 301toward the xiphoid process.

As shown, the lead 310 may include a series of interconnected segments.For example, the lead 310 includes a parasternal lead segment 326, aparasternal electrode segment 328, a first lead segment 330, a firstelectrode segment 332, a second lead segment 334, and a second electrodesegment 336. The parasternal lead segment 326 and the first and secondlead segments 330, 334 represent non-active portions of the lead 310.The parasternal electrode segment 328 has a proximal end 327 and adistal end 329. The first electrode segment 332 has a proximal end 331and a distal end 333. The second electrode segment 336 has a proximalend 335 and a distal end 337.

The parasternal lead segment 326 extends from the pulse generator 304 tothe parasternal electrode segment 328. The parasternal electrode segment328 is positioned subcutaneously and extends extra-thoracically alongone side of the sternum (e.g., left side of patient) to the first leadsegment 330. The first lead segment 330 extends from the parasternalelectrode segment 328 to the first electrode segment 332. The firstelectrode segment 332 is positioned subcutaneously at a level thatapproximately aligns with an apex of a heart of the patient. Theproximal end 331 of the first electrode segment 332 is located proximateto the xiphoid process and/or a mid-sternal line. The first electrodesegment 332 has an active length that extends between the proximal end331 and the distal end 333. For example, the active length in someembodiments is between 5 cm and 12 cm. In more particular embodiments,the active length is between 5 cm and 8 cm.

The second lead segment 334 extends between and joins the firstelectrode segment 332 and the second electrode segment 336. A length ofthe second lead segment 334 may be based on desired positions and activelengths of the first and second electrode segments 332, 336. As shown,each of the first electrode segment 332, the second lead segment 334,and the second electrode segment 336 are positioned within the sameintercostal gap.

The second electrode segment 336 is positioned subcutaneously at a levelthat approximately aligns with an apex of a heart of the patient. Forexample, each of the electrode segments 330, 336 may be positioned at orbelow the apex of the heart. As shown, the second electrode segment 336extends from the proximal end 335, which is positioned at ananterior-lateral location, to the distal end 337, which is positioned ata posterior location. More specifically, the second electrode segment336 extends within an intercostal gap along a side or lateral portion ofthe chest and extends toward a tip or inferior angle of the scapula. Thesecond electrode segment 336 has an active length that extends betweenthe proximal end 335 and the distal end 337. For example, the activelength of the second electrode segment 336, in some embodiments, may beat least 12 cm (e.g., 15 cm). In other embodiments, the second electrodesegment 336 may extend further along the posterior (e.g., toward thescapula) and/or further along the anterior (e.g., begin closer to thefirst electrode segment 332).

During operation, the PG electrode 305 and the parasternal electrodesegment 328 may function as shocking electrodes, and the first electrodesegment 332 and the second electrode segment 336 may be electricallycommon (have the same polarity). A shock vector is indicated by thearrows in FIG. 5. Alternatively, the parasternal electrode segment 328may be sensing electrode.

FIG. 6 illustrates a flow chart of a method 400 for implanting asubcutaneous implantable medical system in accordance with anembodiment. The subcutaneous implantable medical system may be similaror identical to the subcutaneous implantable medical systems describedherein. The method 400 includes implanting, at 402, a pulse generator(PG) subcutaneously within a pectoral region of a chest of a patient.The PG has a housing that includes a PG electrode. For example,implanting, at 402, may include making an incision, at 404, in the chestof the patient. The incision may be performed in a pectoral region, suchas a left pectoral region, and based on the anatomical location of theheart. For instance, the incision may be made approximately 2-4 cm belowthe clavicle, extending from the mid-clavicular region to proximate toand above the humeral-pectoral groove. The lateral extent of theincision may be based on a size of the pulse generator.

At 405, a pocket may be formed. The pocket may be subcutaneous orsubmuscular. The pocket may be completed before or after positioning thelead as described below. For subcutaneous pockets, the subcutaneoustissue may be dissected or separated from the pectoral fascia using adesignated tool (e.g., knife). In some embodiments, an inflatableballoon may be inserted through the incision and inflated to displacethe subcutaneous tissue. For submuscular pockets, the transverse musclefibers of the pectoralis major may be separated for providing access infront of the pectoralis minor. The pulse generator may be positionedwithin the pocket before or after lead placement.

The method also includes implanting, at 406, at least one lead havingfirst and second electrode segments. The implanting, at 406, may includemaking an access incision, at 408 and, optionally, making one or moreother access incisions at 410. Access incisions may be used tomanipulate the lead for placing the first and second electrode segmentsat designated positions. The access incision made at 408 may beproximate to the xiphoid process. The access incision(s) made at 410 maybe along a side and/or posterior of the patient.

Implanting, at 406, may also include tunneling, at 412, a tract betweenthe different incisions and advancing the lead through the tract. Forexample, a tunneling device (e.g., elongated tube) may be insertedthrough the first access incision (e.g., the xiphoid incision). Thetunneling device separates the subcutaneous tissue from underlyingtissue (e.g., muscle, bone) between the first access incision and thepocket. When an end of the tunneling device is accessible through thepocket, a distal end of the lead may be coupled to the end of thetunneling device (e.g., through a suture loop). The tunneling device isthen withdrawn from the first access incision, thereby pulling the leadthrough the newly-formed tract between the pocket and the first accessincision. Subsequently, the tunneling device may be inserted through thesecond access incision and advanced toward the first access incisionalong an intercostal gap. When the end of the tunneling device isaccessible through the first access incision, the lead may be coupled tothe end of the tunneling device. The tunneling device is then withdrawnfrom the second access incision, thereby pulling the lead through thenewly-formed tract between the first access incision and the secondaccess incision. This process may be repeated as necessary forpositioning the lead. Although the above describes moving the lead fromthe pocket to a final access incision (e.g., posterior incision), theprocess may be performed in reverse such that the lead is moved from thefinal access incision (e.g., posterior incision) toward the pocket.

After positioning the first and second electrode segments, the pulsegenerator may be connected to the lead at 416. More specifically, an endportion of the lead may be inserted into a port of the pulse generator.Optionally, the lead may include a parasternal electrode segment. Insuch embodiments, the method may include positioning the parasternalelectrode segment along the sternum.

The method may also include initiating (e.g., activating) the pulsegenerator, at 418. For example, an external device (e.g., programmer)may be communicatively coupled to the pulse generator. The pulsegenerator may communicate identification data to the pulse generator(e.g., obtain model and seal number). The external device may generate achart that correlates to the patient having the pulse generator. Theexternal device may instruct the pulse generator to perform an electrodeintegrity check and measure parameters of the electrodes (e.g.,impedance of shock electrode(s)). The external device and/or the pulsegenerator may determine a sensing configuration for the pulse generatorbased on cardiac activity. During initiation of the pulse generator, at418, therapy parameters may be selected by the user.

Optionally, the pulse generator may be implemented with the hardware,firmware and other components of one or more of implantable medicaldevices (IMDs) that include neurostimulator devices, implantableleadless monitoring and/or therapy devices, and/or alternativeimplantable medical devices, although implemented as a subcutaneousimplantable medical device. For example, the SIMD may represent acardioverter, cardiac rhythm management device, defibrillator,neurostimulator, leadless monitoring device, leadless pacemaker and thelike. For example, the IMD may include one or more structural and/orfunctional aspects of the device(s) described in U.S. Pat. No. 9,333,351“Neurostimulation Method And System To Treat Apnea” and U.S. Pat. No.9,044,610 “System And Methods For Providing A Distributed VirtualStimulation Cathode For Use With An Implantable NeurostimulationSystem”, which are hereby incorporated by reference. Additionally oralternatively, the IMD may include one or more structural and/orfunctional aspects of the device(s) described in U.S. Pat. No. 9,216,285“Leadless Implantable Medical Device Having Removable And FixedComponents” and U.S. Pat. No. 8,831,747 “Leadless NeurostimulationDevice And Method Including The Same”, which are hereby incorporated byreference. Additionally or alternatively, the IMD may include one ormore structural and/or functional aspects of the device(s) described inU.S. Pat. No. 8,391,980 “Method And System For identifying A PotentialLead Failure In An implantable Medical Device” and U.S. Pat. No.9,232,485 “System And Method For Selectively Communicating With AnImplantable Medical Device”, which are all hereby incorporated byreference in their entireties.

At 419, a defibrillation test may be performed to determine adefibrillation threshold. The test may be administered prior to or afterclosing the incision. The defibrillation threshold is a quantitativeestimate of the ability of the heart to defibrillate. The defibrillationthreshold is typically defined as the minimum shock strength that causesdefibrillation. The defibrillation threshold can be measured by changingthe voltages in subsequent VF inductions in accordance with apredetermined protocol. For example, the stored voltages may beincrementally decreased for subsequent VF inductions until the firstshock is unable to defibrillate. This is referred to as a step-down tofailure test. If a high defibrillation threshold is identified, it maybe desirable to make adjustments to the system. For example, the leadscould be repositioned, the leads could be switched-out, portions of theelectrodes could be capped, or another lead may be added. Thedefibrillation testing may be performed using an external device (e.g.,programmer) that is communicatively coupled to the pulse generator.

Another defibrillation test may including applying the same energytwice. The first electrical shock may be programmed to deliver anamplitude that is less than 10 Joules from the maximum capacity of thesystem. To verify the effectiveness of the shock, the same amplitude maythen be applied a second time. At least three to five minutes mayseparate subsequent applications to allow hemodynamic recovery and tominimize the cumulative effect of the electrical shocks. If theelectrical shock delivered by the it defibrillator is ineffective, arescue shock can be delivered either by an external defibrillator orthrough the implanted defibrillator.

After closing the incisions, the method may also include sensing cardiacactivity at 420 and analyzing, at 421, the cardiac activity to determinewhether a cardiac event-of-interest has occurred. In response todetermining that a cardiac event-of-interest has occurred, a therapy maybe applied, at 422. For example, the pulse generator may sensesubcutaneous signals (e.g., subcutaneous ECG signals) and a cardiacrhythm using a combination of the electrodes. The pulse generator mayprocess the cardiac signals (e.g., filter and/or amplify) and analyzethe cardiac activity to determine whether an event that requires therapyis occurring. If the pulse generator determines that a cardiacevent-of-interest is occurring, such as ventricular fibrillation,ventricular tachycardia, or other arrhythmia, the pulse generator mayapply therapy (e.g., electrical shock) to the heart using a combinationof the electrodes.

FIG. 7 illustrates a block diagram of an SIMD. The SIMD is capable ofperforming stimulation therapy, including cardioversion, defibrillation,and pacing stimulation. The SIMD is hereinafter referred to as thedevice 601. While a particular multi-element device is shown, this isfor illustration purposes only. It is understood that the appropriatecircuitry could be duplicated, eliminated or disabled in any desiredcombination to provide a device capable of monitoring impedance and/orcardiac signals, and/or treating the appropriate chamber(s) withcardioversion, defibrillation and pacing stimulation.

The housing 640 for the device 601 is often referred to as the“canister,” “can,” “case,” or “case electrode” and may be programmablyselected to act as the shock electrode and/or as a return electrode forsome or all sensing modes. The housing 640 may further be used as areturn electrode alone or in combination with one or more otherelectrodes. The housing 640 further includes a connector (not shown)having a plurality of terminals 647-652. To achieve sensing, pacing, andshocking in connection with desired chambers of the heart, the terminals647-652 are selectively connected to corresponding combinations ofelectrodes.

The device 601 includes a programmable microcontroller 660 that controlsthe various modes of sensing and stimulation therapy. Themicrocontroller 660 includes a microprocessor, or equivalent controlcircuitry, designed specifically for controlling sensing impedancederivation and the delivery of stimulation therapy and may furtherinclude RAM or ROM memory, logic and timing circuitry, state machinecircuitry, and I/O circuitry. The microcontroller 660 includes theability to process or monitor input signals (data) as controlled by aprogram code stored in memory. The details of the design and operationof the microcontroller 660 are not critical to the present invention.Rather, any suitable microcontroller 660 may be used.

The microcontroller 660 includes inputs that are configured to collectcardiac signals associated with electrical or mechanical behavior of aheart over at least one cardiac cycle. The cardiac signals may be fromthe cardiac sensing circuit 682 and representative of electricalbehavior of the heart. The circuit 682 may provide separate, combined,composite or difference signals to the microcontroller 660representative of the sensed signals from the electrodes. Optionally,the cardiac signals may be the output of the A/D circuit 690 that arerepresentative of electrical behavior of the heart. The cardiac signalsmay be the output of the physiologic sensor 607 that are representativeof mechanical behavior.

The microcontroller 660 includes a cardiac signal (CS) module 661, amarker detection (MD) module 663 and a therapy module 665 (among otherthings). The CS module 661 is configured to analyze cardiac signals. TheMD module 663 is configured to analyze signals sensed over the markersensing channel and identify incoming event markers. The therapy module665 is configured to modulate, over multiple cardiac cycles; at leastone therapy parameter while the device 601 obtains a collection of atleast one CSF indicators associated with different therapy parameters.The therapy module 665 is further configured to adjust a therapyconfiguration based on, among other things, the cardiac signals andbased on the event markers.

The microcontroller 660 further controls a shocking circuit 617 by wayof a control signal. The shocking circuit 617 generates stimulatingpulses of low (up to 0.5 Joules), moderate (0.5-10 Joules), or highenergy (11 to 50 Joules), as controlled by the microcontroller 660.Stimulating pulses may be applied to the patient's heart through atleast two shocking electrodes.

One or more pulse generators 670 and 672 generate various types oftherapy, such as pacing and ATP stimulation pulses for delivery bydesired electrodes. The electrode configuration switch 674 (alsoreferred to as a switch bank) controls which terminals 647-652 areconnected to the pulse generators 670, 672, thereby controlling whichelectrodes receive a therapy. The pulse generators, 670 and 672, mayinclude dedicated, independent pulse generators, multiplexed pulsegenerators, shared pulse generators or a single common pulse generator.The pulse generators 670 and 672 are controlled by the microcontroller660 via appropriate control signals to trigger or inhibit stimulationpulses. The microcontroller 660 further includes timing controlcircuitry which is used to control the timing of such stimulation pulses(e.g., pacing rate, atrio-ventricular (AV) delay, atrial interconduction(A-A) delay, or ventricular interconduction (V-V) delay, etc.) as wellas to keep track of the timing of refractory periods, PVARP intervals,noise detection windows, evoked response windows, alert intervals,marker channel timing, etc.

An electrode configuration switch 674 connects the sensing electronicsto the desired terminals 647-652 of corresponding sensing electrodes.For example, a portion of the terminals may be coupled to electrodesconfigured to define a sensing and/or shocking vector that passesthrough the left ventricle. The electrode configuration switch 674 mayconnect terminals to the event marker sensing circuit 684 (whichcorresponds to the event marker sensing channel) and themicrocontroller. The circuit 684 may amplify, filter, digitize and/orotherwise process the sensed signals from the select electrodes.

The electrode configuration switch 674 also connects variouscombinations of the electrodes to an impedance measuring circuit 613.The impedance measuring circuit 613 includes inputs to collect multiplemeasured impedances between corresponding multiple combinations ofelectrodes. For example, the impedance measuring circuit 613 may collecta measured impedance for each or a subset of the active sensing vectors.Optionally, the impedance measuring circuit 613 may measure respirationor minute ventilation; measure thoracic impedance for determining shockthresholds; detect when the device has been implanted; measure strokevolume; and detect the opening of heart valves, etc.

The electrode configuration switch 674 includes a plurality of switchesfor connecting the desired electrodes to the appropriate I/O circuits,thereby providing complete electrode programmability. The electrodeconfiguration switch 674, in response to a control signal from themicrocontroller 660, determines the polarity of the stimulation pulses(e.g., unipolar, bipolar, co-bipolar, etc.) by selectively closing theappropriate combination of switches (not specifically shown). Theoutputs of the cardiac sensing and event marker sensing circuits 682 and684 are connected to the microcontroller 660 which, in turn, is able totrigger or inhibit the pulse generators 670 and 672, respectively. Thesensing circuits 682 and 684, in turn, receive control signals from themicrocontroller 660 for purposes of controlling the gain, threshold, thepolarization charge removal circuitry (not shown), and the timing of anyblocking circuitry (not shown).

Cardiac signals are also applied to the inputs of an analog-to-digital(A/D) data acquisition system 690. The data acquisition system 690 isconfigured to acquire cardiac signals, convert the raw analog data intoa digital signal, and store the digital signals for later processingand/or telemetric transmission to an external device 610 (e.g.,programmer). The data acquisition system 690 samples cardiac signalsacross any pair of desired electrodes. The data acquisition system 690may be coupled to the microcontroller 660, or other detection circuitry,for detecting an evoked response from the heart in response to anapplied stimulus, thereby aiding in the detection of “capture.” Captureoccurs when an electrical stimulus applied to the heart is of sufficientenergy to depolarize the cardiac tissue, thereby causing the heartmuscle to contract.

The microcontroller 660 is further coupled to a memory 694 by a suitabledata/address bus 696. The memory 694 stores programmable operating,impedance measurements, impedance derivation and therapy-relatedparameters used by the microcontroller 660. The operating andtherapy-related parameters define, for example, pacing pulse amplitude,pulse duration, electrode polarity, rate, sensitivity, automaticfeatures, arrhythmia detection criteria, and the amplitude, wave shapeand vector of each stimulating pulse to be delivered to the patient'sheart within each respective tier of therapy.

The operating and therapy-related parameters may be non-invasivelyprogrammed into the memory 694 through a telemetry circuit 600 intelemetric communication with the external device 610, such as aprogrammer, trans-telephonic transceiver, or a diagnostic systemanalyzer. The telemetry circuit 600 is activated by the microcontroller660 by a control signal. The telemetry circuit 600 advantageously allowsdata and status information relating to the operation of the device (ascontained in the microcontroller 660 or memory 694) to be sent to anexternal device through an established communication link 603.

The device 601 may include a physiologic sensor 607 to adjust pacingstimulation rate according to the exercise state of the patient. Thephysiological sensor 607 may further be used to detect changes incardiac output, changes in the physiological condition of the heart, ordiurnal changes in activity (e.g., detecting sleep and wake states). Thebattery 611 provides operating power to all of the circuits shown inFIG. 7.

It will be readily understood that the components of the embodiments asgenerally described and illustrated in the Figures herein, may bearranged and designed in a wide variety of different configurations inaddition to the described example embodiments. Thus, the following moredetailed description of the example embodiments, as represented in theFigures, is not intended to limit the scope of the embodiments, asclaimed, but is merely representative of example embodiments.

Reference throughout this specification to “one embodiment” or “anembodiment” (or the like) means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, appearances of the phrases “in oneembodiment” or “in an embodiment” or the like in various placesthroughout this specification are not necessarily all referring to thesame embodiment.

Furthermore, the described features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments. In thefollowing description, numerous specific details are provided to give athorough understanding of embodiments. One skilled in the relevant artwill recognize, however, that the various embodiments can be practicedwithout one or more of the specific details, or with other methods,components, materials, etc. In other instances, well-known structures,materials, or operations are not shown or described in detail to avoidobfuscation. The following description is intended only by way ofexample, and simply illustrates certain example embodiments.

It is to be understood that the above description is intended to beillustrative, and not restrictive. For example, the above-describedembodiments (and/or aspects thereof) may be used in combination witheach other. In addition, many modifications may be made to adapt aparticular situation or material to the teachings of the inventivesubject matter without departing from its scope. While the dimensionsand types of materials described herein are intended to define theparameters of the inventive subject matter, they are by no meanslimiting and are exemplary embodiments. Many other embodiments will beapparent to one of ordinary skill in the art upon reviewing the abovedescription. The scope of the inventive subject matter should,therefore, be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled. Inthe appended claims, the terms “including” and “in which” are used asthe plain-English equivalents of the respective terms “comprising” and“wherein.” Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects. Further, thelimitations of the following claims are not written inmeans-plus-function format and are not intended to be interpreted basedon 35 U.S.C. § 112(f) unless and until such claim limitations expresslyuse the phrase “means for” followed by a statement of function void offurther structure.

What is claimed is:
 1. A method comprising: implanting a pulse generator(PG) within a pectoral region of a chest of a patient, the PG having ahousing that includes a PG electrode; and implanting at least one leadhaving first and second electrode segments with the first electrodesegment positioned along an anterior of the chest of the patient and thesecond electrode segment positioned along at least one of a posterior ofthe patient or a side of the patient, the first and second electrodesegments being positioned subcutaneously at or below an apex of a heartof the patient, wherein the PG electrode and the first and secondelectrode segments are configured to provide electrical shocks forantiarrhythmic therapy, wherein implanting the second electrode segmentincludes making a tunnel that extends along an intercostal gap between afirst access incision proximate to a xiphoid process and a second accessincision that is positioned at or beyond a midaxillary line.
 2. Themethod of claim 1, wherein the first and second electrode segments areportions of a common lead coil that extends from a proximal end of thefirst electrode segment to a distal end of the second electrode segment,the common lead coil extending along the chest of the patient from theanterior of the chest toward the side of the patient, wherein the secondelectrode segment extends to or beyond a midaxillary line of thepatient.
 3. The method of claim 2, wherein an active length of thecommon lead coil is at least 35 cm from the proximal end of the firstelectrode segment to the distal end of the second electrode segment. 4.The method of claim 1, wherein the first and second electrode segmentsare spaced apart from one another, the second electrode segment beinglonger than the first electrode segment.
 5. The method of claim 4,wherein the second electrode segment has an active length measuredbetween proximal and distal ends of the second electrode segment, theactive length being at least 12 centimeters (cm), wherein the secondelectrode segment extends beyond a posterior axillary line.
 6. Themethod of claim 1, wherein implanting the at least one lead includespositioning one lead such that the one lead extends away from the pulsegenerator, extra-thoracically along a sternum, and along an intercostalgap so that a distal end of the one lead is positioned at or beyond amidaxillary line of the patient.
 7. The method of claim 1, whereinimplanting the first electrode segment includes tunneling from a pocketwhere the pulse generator is positioned along a sternum of the patientto an intercostal gap at or below the apex of the heart.
 8. The methodof claim 1, wherein implanting the pulse generator includes making asubcutaneous pocket and positioning the pulse generator within thesubcutaneous pocket.
 9. The method of claim 1, wherein the first andsecond electrode segments are portions of a continuous elongated bodythat wraps about the patient, wherein implanting the first electrodesegment and the second electrode segment includes making a xiphoidincision and an access incision at or beyond a midaxillary line near anintercostal gap.
 10. The method of claim 1, wherein the first electrodesegment has an active length extending between a proximal end and adistal end of the first electrode segment, the active length beingbetween 5 and 12 cm.
 11. The method of claim 1, wherein a defibrillationthreshold (DFT) is at most 50 Joules and a volume of the pulse generatoris at most 40 milliliters.
 12. The method of claim 1, wherein the firstand second electrode segments are portions of a common lead coil thatextends from a proximal end of the first electrode segment to a distalend of the second electrode segment, the common lead coil having anactive length that is at least 35 cm from the proximal end of the firstelectrode segment to the distal end of the second electrode segment, thecommon lead coil extending along the chest of the patient from theanterior of the chest toward the side of the patient and extending to orbeyond a midaxillary line of the patient, the pulse generator operableto generate a defibrillating energy of at most 50 Joules.
 13. A methodcomprising: implanting a pulse generator (PG) within a pectoral regionof a chest of a patient, the PG having a housing that includes a PGelectrode; implanting at least one lead having first and secondelectrode segments with the first electrode segment positioned along ananterior of the chest of the patient and the second electrode segmentpositioned along at least one of a posterior of the patient or a side ofthe patient, the first and second electrode segments being positionedsubcutaneously at or below an apex of a heart of the patient, whereinthe PG electrode and the first and second electrode segments areconfigured to provide electrical shocks for antiarrhythmic therapy; andinitiating the pulse generator and sensing cardiac activity, wherein thepulse generator is configured to analyze the cardiac activity andprovide therapy in response to identifying a cardiac event-of-interestusing the cardiac activity.
 14. A subcutaneous implantable medicalsystem comprising: a pulse generator (PG) configured to be positionedsubcutaneously within a pectoral region of a chest of a patient, the PGhaving a housing that includes a PG electrode, the PG having anelectronics module; and an elongated lead that is electrically coupledto the pulse generator, the elongated lead including a first electrodesegment that is configured to be positioned along an anterior of thechest of the patient and a second electrode segment that is configuredto be positioned along at least one of a posterior of the patient or aside of the patient, wherein an active length of the elongated leadextends between a proximal end of the first electrode segment and adistal end of the second electrode segment, the active length being atleast 35 centimeters (cm), wherein the electronics module is configuredto provide electrical shocks for antiarrhythmic therapy using the PGelectrode and the first and second electrode segments.
 15. Thesubcutaneous implantable medical system of claim 14, wherein the firstand second electrode segments are portions of a common lead coil thatextends from the proximal end of the first electrode segment to thedistal end of the second electrode segment, the common lead coil beingsized to extend along the chest of the patient from the anterior of thechest to the posterior of the patient, an active length of the commonlead coil being at least 35 cm from the proximal end of the firstelectrode segment to the distal end of the second electrode segment. 16.The subcutaneous implantable medical system of claim 14, wherein thefirst and second electrode segments are spaced apart from one another,the second electrode segment being longer than the first electrodesegment, the second electrode segment having an active length measuredbetween proximal and distal ends of the second electrode segment, theactive length being at least 12 cm, wherein the second electrode segmentextends beyond a posterior axillary line.
 17. The subcutaneousimplantable medical system of claim 14, wherein the first electrodesegment has an active length measured between proximal and distal endsof the first electrode segment, the active length being between 5 and 12cm.
 18. The subcutaneous implantable medical system of claim 14, whereina defibrillation threshold (DFT) is at most 50 Joules and a volume ofthe PG is at most 40 milliliters.
 19. A method of treating a patient,the method comprising: sensing cardiac activity of a patient with asubcutaneous implantable medical system, the subcutaneous implantablemedical system including a pulse generator (PG) positionedsubcutaneously within a pectoral region of a chest of the patient, thesubcutaneous implantable medical system also including a first electrodesegment positioned along an anterior of the chest of the patient and asecond electrode segment positioned along at least one of a posterior ofthe patient or a side of the patient, the first and second electrodesegments being positioned subcutaneously at or below an apex of a heartof the patient, wherein the first and second electrode segments areportions of a common lead coil that extends from a proximal end of thefirst electrode segment to a distal end of the second electrode segment,the common lead coil extending along the chest of the patient from theanterior of the chest to the posterior of the patient, an active lengthof the common lead coil being at least 35 cm from the proximal end ofthe first electrode segment to the distal end of the second electrodesegment; and providing antiarrhythmic therapy, based on the cardiacactivity, by providing electrical shocks or pulses between the first andsecond electrode segments and an electrode of the PG.
 20. The method ofclaim 19, wherein the first and second electrode segments are spacedapart from one another, the second electrode segment being longer thanthe first electrode segment, the second electrode segment having alength that is at least 12 centimeters (cm), wherein a defibrillationthreshold (DFT) is at most 50 Joules and a volume of the PG is at most40 milliliters.
 21. The method of claim 13, wherein the first and secondelectrode segments are portions of a common lead coil that extends froma proximal end of the first electrode segment to a distal end of thesecond electrode segment, the common lead coil extending along the chestof the patient from the anterior of the chest toward the side of thepatient, wherein the second electrode segment extends to or beyond amidaxillary line of the patient.
 22. The method of claim 21, wherein anactive length of the common lead coil is at least 35 cm from theproximal end of the first electrode segment to the distal end of thesecond electrode segment.
 23. The method of claim 13, wherein the firstand second electrode segments are spaced apart from one another, thesecond electrode segment being longer than the first electrode segment,wherein the second electrode segment has an active length measuredbetween proximal and distal ends of the second electrode segment, theactive length being at least 12 centimeters (cm), wherein the secondelectrode segment extends beyond a posterior axillary line.
 24. Themethod of claim 13, wherein implanting the at least one lead includespositioning one lead such that the one lead extends away from the pulsegenerator, extra-thoracically along a sternum, and along an intercostalgap so that a distal end of the one lead is positioned at or beyond amidaxillary line of the patient.
 25. The method of claim 13, whereinimplanting the second electrode segment includes making a tunnel thatextends along an intercostal gap between a first access incisionproximate to a xiphoid process and a second access incision that ispositioned at or beyond a midaxillary line.
 26. The method of claim 19,wherein the first and second electrode segments are portions of acontinuous elongated body that wraps about the patient, and the firstelectrode segment and the second electrode segment are implanted bymaking a xiphoid incision and an access incision at or beyond amidaxillary line near an intercostal gap.
 27. The method of claim 19,wherein the first electrode segment has an active length extendingbetween a proximal end and a distal end of the first electrode segment,the active length being between 5 and 12 cm.
 28. The method of claim 19,further comprising implanting the second electrode segment by making atunnel that extends along an intercostal gap between a first accessincision proximate to a xiphoid process and a second access incisionthat is positioned at or beyond a midaxillary line.